全文获取类型
收费全文 | 292935篇 |
免费 | 2933篇 |
国内免费 | 1070篇 |
专业分类
电工技术 | 5430篇 |
综合类 | 2511篇 |
化学工业 | 41906篇 |
金属工艺 | 15563篇 |
机械仪表 | 13493篇 |
建筑科学 | 7523篇 |
矿业工程 | 1656篇 |
能源动力 | 5591篇 |
轻工业 | 21237篇 |
水利工程 | 3109篇 |
石油天然气 | 2458篇 |
武器工业 | 5篇 |
无线电 | 34886篇 |
一般工业技术 | 60673篇 |
冶金工业 | 32239篇 |
原子能技术 | 3646篇 |
自动化技术 | 45012篇 |
出版年
2018年 | 21432篇 |
2017年 | 21152篇 |
2016年 | 14095篇 |
2015年 | 2114篇 |
2014年 | 2100篇 |
2013年 | 6875篇 |
2012年 | 8212篇 |
2011年 | 20348篇 |
2010年 | 18004篇 |
2009年 | 15421篇 |
2008年 | 16381篇 |
2007年 | 19295篇 |
2006年 | 4592篇 |
2005年 | 8758篇 |
2004年 | 6837篇 |
2003年 | 6433篇 |
2002年 | 5018篇 |
2001年 | 4159篇 |
2000年 | 4053篇 |
1999年 | 3815篇 |
1998年 | 6909篇 |
1997年 | 5397篇 |
1996年 | 4604篇 |
1995年 | 3792篇 |
1994年 | 3458篇 |
1993年 | 3296篇 |
1992年 | 2833篇 |
1991年 | 2755篇 |
1990年 | 2660篇 |
1989年 | 2643篇 |
1988年 | 2498篇 |
1987年 | 2198篇 |
1986年 | 2141篇 |
1985年 | 2584篇 |
1984年 | 2351篇 |
1983年 | 2230篇 |
1982年 | 2100篇 |
1981年 | 2022篇 |
1980年 | 1876篇 |
1979年 | 1893篇 |
1978年 | 1796篇 |
1977年 | 2112篇 |
1976年 | 2607篇 |
1975年 | 1609篇 |
1974年 | 1447篇 |
1973年 | 1476篇 |
1972年 | 1213篇 |
1971年 | 1123篇 |
1970年 | 949篇 |
1968年 | 890篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
D. V. V. Satyanarayana G. Malakondaiah D. S. Sarma 《Metallurgical and Materials Transactions A》2003,34(11):2579-2590
The effect of prior oxidation at 1473 K on the creep behavior of an Fe-Ni-Cr-Al alloy, hardened by ordered NiAl precipitates,
has been investigated at 873 K over a stress range of 275 to 450 MPa. The alloy in the as-electroslag remelted (ESR) as well
as the ESR-plus-hot-worked conditions was considered. Prior oxidation causes creep strengthening in the Fe-Ni-Cr-Al alloy,
resulting in a decrease in minimum creep rate and increase in time to rupture, in contrast to the observations reported on
nickel-based superalloys. Creep strengthening is, however, accompanied by a significant reduction in creep ductility. Oxidation-induced
creep strengthening in the current alloy can be attributed to the improved adherence of surface oxide caused by the presence
of yttrium. An effective stress that incorporates the contributions of load transfer as well as substructural strengthening
is used to account for the observed oxidation-induced creep strengthening. While creep strengthening is more pronounced in
the ESR cast alloy, the loss in creep ductility is more intense in the ESR wrought alloy. Increasing the oxidation time beyond
1 hour has a minimal effect on creep strengthening of both the alloys, though it lowers significantly the creep ductility
of the wrought alloy. The observed differences in creep behavior of the alloy in the two different conditions could be attributed
to the differences in grain size as well as morphology and related oxidation-induced damage. 相似文献
962.
N. E. Shchepina V. V. Avrorin G. A. Badun V. M. Fedoseev S. E. Ukhanov S. B. Lewis 《Radiochemistry》2007,49(6):630-632
Ion-molecule reactions of free phenyl cations with six-membered nitrogen-containing heterocyclic compounds: α-, β-, and γ-picolines, were studied. Phenyl cations were generated by tritium β-decay in double-labeled benzene. The mechanism of competing reactions of electrophilic addition to the nitrogen heteroatom in the ring and electrophilic substitution of the C-H bond in the pyridine ring was examined. The effect of methyl substituent in the pyridine molecule on the reaction pathway was evaluated. A one-step procedure for nuclear-chemical synthesis of tritium-labeled N-phenylpicolinium salts and phenyl-substituted picolines was developed. 相似文献
963.
964.
L. K. Isaev 《Measurement Techniques》2007,50(11):1214-1217
The main prerequisites are considered in a historical aspect and steps ate taken in creating a world-wide metrology system
with the aim of providing conditions for the mutual recognition of measurement results.
__________
Translated from Izmeritel’naya Tekhnika, No. 11. pp. 59–62, November, 2007. 相似文献
965.
The behavior of hydrogen in solids under the action of intense ionizing radiation is of importance in solving numerous problems of materials science for the nuclear and thermonuclear power industry, spacecraft engineering, hydrogen energetics, and microelectronics. Experimental results are presented that provide evidence of the radiation-induced yield of hydrogen from single crystal silicon bombarded with 710-MeV bismuth ions. 相似文献
966.
J. Lub W.P.M. Nijssen R.T. Wegh J.P.A. Vogels A. Ferrer 《Advanced functional materials》2005,15(12):1961-1972
This paper describes the synthesis of photoisomerizable derivatives of isosorbide. These derivatives contain a stilbene or cinnamate moiety and can therefore be used as photoisomerizable chiral compounds in cholesteric liquid‐crystalline mixtures. The reflection wavelength of cholesteric layers made from these mixtures is increased by UV irradiation due to the fact that the Z‐isomers of these derivatives exhibit a lower helical twisting power than the corresponding E‐isomers. The cinnamate derivatives are very suitable for use in cholesteric color filters that find application in liquid‐crystal displays. 相似文献
967.
J.-G. Kim W.-P. Tai Y.-J. Kwon K.-J. Lee W.-S. Cho N.-H. Cho C.M. Whang Y.-C. Yoo 《Journal of Materials Science: Materials in Electronics》2004,15(12):807-811
Donor doped BaTiO3 (n-BaTiO3) ceramics were fabricated by adding polyethylene glycol (PEG) at 20 wt %. The effects of reducing and oxidizing atmospheres on the PTCR characteristics of the porous n-BaTiO3 ceramics were investigated. The PTCR characteristics of the porous n-BaTiO3 ceramics is strongly affected by chemisorbed oxygen at the grain boundaries and are recovered as the atmosphere is changed from the reducing gas to oxidizing gas. The low room-temperature resistivity of the porous n-BaTiO3 ceramics in reducing atmospheres may be caused by the decrease in potential barrier height, which originates from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In addition, the high room-temperature resistivity of the porous n-BaTiO3 ceramics in oxidizing atmospheres may be caused by the increase in potential barrier height, which results from the adsorption of chemisorbed oxygen atoms at the grain boundaries. 相似文献
968.
O'Keefe M.F. Atherton J.S. Bosch W. Burgess P. Cameron N.I. Snowden C.M. 《Semiconductor Manufacturing, IEEE Transactions on》2003,16(3):376-383
The establishment of a 150-mm (6-in) gallium arsenide (GaAs) facility is described together with the development of very high yielding and cost-effective semiconductor device technologies and a manufacturing capacity of over 40000 wafers/annum. The background to the demand for very high volumes of RF products for this market is discussed, together with the prospects for future growth. The paper describes recent process development by the utilization of a data-driven yield management system to support the delivery of high-quality RF products to customers. Finally, "end of line" DC and RF testing of finished 150-mm GaAs pHEMT foundry wafers is described, enabling scalar measurements of power, noise, and intermodulation products as well as vector measurements of S-parameters and noise parameters at frequencies of up to 40 GHz. 相似文献
969.
The paper investigates the performance of various time stepping schemes for coupled displacement and pore pressure analysis.
A number of alternative forms of the automatic time stepping method proposed by Sloan and Abbo (1999a) are also presented.
These alternative schemes use different updates for the displacements and pore pressures and also adopt different starting
conditions for the iterations. The automatic schemes are compared with an implicit θ-method, as well as an explicit method,
through analysis of a variety of problems involving undrained loading, drained loading, and consolidation for Mohr-Coulomb
and critical state models. As expected, the numerical results confirm that the explicit scheme is neither accurate nor robust.
Although the implicit θ-method is accurate and fast, it fails to give a solution in a number of cases where the time step
is large. The automatic schemes are shown to be accurate, fast and generally robust. Two of the automatic schemes proposed
never fail to furnish a solution for the cases considered. In addition, all the automatic schemes are able to constrain the
time-stepping (temporal integration) error in the displacements and pore pressures to lie near a prescribed tolerance, provided
the iteration error tolerance is properly chosen. For complex soil models, it is important that the latter is set sufficiently
small in order for the schemes to be able to constrain the time-stepping error to lie within a prescribed tolerance.
Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and cooperation as a colleague and friend over many
years. 相似文献
970.
J. Gajdoš Kljusurić 《Sadhana》2003,28(6):991-998
This work is an experimental study of the differential scanning calorimetry characterisation of polymer materials used in
food packaging materials, such as polypropylene (0.03 mm), polyethylene (0.1 and 0.03 mm), poly(D-(-)-Β-hydroxybutyrate) (powder),
two-layered polypropylene (0.064 mm), and two-layered polypropylene with poly-vinylidene-chloride (0.012/0.021). The polymer
stability was checked by simulation of conditions during food preparation in microwave ovens, sterilisation or rapid freezing.
The materials were tested in the temperature range from 40 to 200‡C at different scan rates from 2 to 30°C min−1 during heating or cooling. The enthalpies show a high correlation coefficient (0.964) with scan rate. All samples undergo
phase change in the temperature range from 107 to 173°C during heating and enthalpies are in the range from 31.8 to 71.1Jg−1. Upon subsequent cooling from 200°C, the temperature range of phase changes is shifted to lower temperatures from 86 to 102°C
with enthalpies ranging from 30.4 to 57.8 J g−1.
Experiments with exposure of polymers to microwave radiation and freezing prove that the phase change considering the temperature
range is very similar in all experiments. 相似文献